The present invention relates generally to fuel system control techniques, and more specifically to techniques for diagnosing failures and fault conditions in a fuel system.
Electronically controlled high pressure fuel systems are known and commonly used in the automotive and heavy duty truck industries. Such systems may include a fuel pump operable to provide high pressure fuel to a collection unit that supplies the pressurized fuel to one or more fuel injectors. One or more pressure sensors are typically provided for monitoring and controlling the fuel pressure throughout the system.
An example of one such system is described in U.S. Pat. No. 5,678,521 to Thompson et al., which is assigned to the assignee of the present invention. The Thompson et al. fuel system includes a pair of cam driven high pressure fuel pumps operable to pump fuel from a low pressure fuel source to an accumulator. The accumulator passes the high pressure fuel to a single injection control valve which is electronically controllable to supply the fuel to a distributor unit. The distributor, in turn, distributes the fuel to any of a number of fuel injectors. The accumulator includes a pressure sensor for monitoring accumulator pressure. An electronic control unit monitors accumulator pressure, throttle position and engine speed, and is operable to control the operation of the fuel system in accordance therewith.
High pressure fuel systems of the type just described, while having many advantages over prior mechanical systems, have certain drawbacks associated therewith. For example, failure of electrical and/or mechanical components of the system may result in total system failure, in which case the engine is often shut down leaving the vehicle and occupant stranded. In severe cases, failure of such components can lead to catastrophic destruction of fuel system components.
What is therefore needed is a system for diagnosing faults and failures in an electronically controlled fuel system of the type just described. Such a system should ideally log fault codes indicative of fuel system related failures to assist in repair efforts, and should additionally provide for one or more limp home fueling operational modes so that the vehicle can be driven out of danger and/or to a repair facility.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, an apparatus for diagnosing a fuel system of an internal combustion engine, comprises a first fuel pump responsive to a pump command signal for supplying high pressure fuel from a lower pressure fuel source, an accumulator receiving the high pressure fuel from the first fuel pump, a valve responsive to a valve control signal for drawing high pressure fuel from the accumulator, means for sensing fuel pressure within the accumulator and producing a pressure signal corresponding thereto, wherein the pressure signal has peak values corresponding to peak pressures of fuel supplied thereto by the first fuel pump and lower valley values corresponding to valley pressures of fuel within the accumulator resulting from fuel drawn therefrom. A control computer is provided for sampling a number of first pressure values each near a separate one of the peak values and a number of second pressure values each near a separate one of the valley values of the pressure signal, and determining an average pressure value based thereon. The control computer is operable to compare each of the number of first and second pressure values to the average pressure value and increment an error counter if at least one of the number of first and second pressure values are outside of a threshold range of the average pressure value.
In accordance with another aspect of the present invention, a method of diagnosing a fuel system of an internal combustion engine comprises the steps of activating a first fuel pump to supply fuel from a fuel source to an accumulator based on a target fuel pressure value, measuring a first pressure value within the accumulator near an actual peak pressure value therein resulting from activation of the first fuel pump, activating a control valve to draw pressurized fuel from the accumulator resulting from activation of the first fuel pump, the accumulator thereafter defining a valley fuel pressure therein, measuring a second pressure value within the accumulator near the valley fuel pressure, determining an average pressure value based on a number of the first and second pressure values, comparing each of the number of first and second pressure values with the average pressure value, and incrementing an error counter if at least one of the number of first and second pressure values are outside of a threshold range of the average pressure value.
In accordance with a further aspect of the present invention, an apparatus for diagnosing a fuel system of an internal combustion engine comprises a first fuel pump responsive to first pump command signals for supplying high pressure fuel from a lower pressure fuel source, an accumulator receiving the high pressure fuel from the first fuel pump, means for sensing fuel pressure within the accumulator and producing a pressure signal corresponding thereto, and a control computer receiving the pressure signal and producing the first pump control signals, the control computer producing a number of first pump command signals corresponding to zero commanded fueling and monitoring first corresponding changes in the pressure signal, the control computer incrementing an error counter if at least one of the first corresponding changes in the pressure signal exceeds a predefined pressure change threshold.
In accordance with yet another aspect of the present invention, a method of diagnosing a fuel system of an internal combustion engine comprises the steps of activating a first fuel pump to supply zero commanded fuel from a fuel source to an accumulator, measuring a first corresponding change in pressure in the accumulator resulting from activation of the first fuel pump with zero commanded fuel, repeating the activating and measuring steps a number of times, comparing each of the number of first corresponding changes in pressure with a pressure change threshold, and incrementing an error counter if at least one of the number of first corresponding changes in pressure exceeds a pressure change threshold.
In accordance with still a further aspect of the present invention, an apparatus for diagnosing a fuel system of an internal combustion engine comprises a first fuel pump responsive to first pump command signals for supplying high pressure fuel from a lower pressure fuel source, a second fuel pump responsive to second pump command signals for supplying high pressure fuel from the lower pressure fuel source, an accumulator receiving the high pressure fuel from the first and second fuel pumps, means for sensing fuel pressure within the accumulator and producing a pressure signal corresponding thereto, and a control computer producing a number of the first and second pump command signals and monitoring first and second corresponding changes in the pressure signal, the control computer determining first and second average pressure change values based on respective ones of the number of first and second corresponding changes in the pressure signal, the control computer incrementing an error counter if a difference between the first and second average pressure change values is one of greater than a first pressure change limit and less than a second pressure change limit.
In accordance with still another aspect of the present invention, a method of diagnosing a fuel system of an internal combustion engine comprises the steps of activating a first fuel pump to supply fuel to an accumulator based on a target fuel pressure value, activating a second fuel pump to supply fuel to the accumulator based on the target fuel pressure value, determining a first pressure change value corresponding to a change in fuel pressure within the accumulator resulting from activation of the first pump, determining a second pressure change value corresponding to a change in fuel pressure within the accumulator resulting from activation of the second pump, repeating the activation steps and the determining steps a number of times, computing a first average pressure change value as an average of the number of first pressure change values, computing a second average pressure change value as an average of the number of second pressure change values, and incrementing an error counter if a difference between the first and second average pressure change values is one of greater than a first pressure change limit and less than a second pressure change limit.
In accordance with yet another aspect of the present invention, an apparatus for diagnosing a fuel system of an internal combustion engine comprises a fuel pump responsive to a pump command signal for supplying high pressure fuel from a lower pressure fuel source, an accumulator receiving the high pressure fuel from the fuel pump, means for producing a fuel demand signal, means for sensing fuel pressure within the accumulator and producing a pressure signal corresponding thereto, means for sensing engine speed and producing an engine speed signal corresponding thereto, and a control computer receiving the pressure, engine speed and fuel demand signals and producing the pump command signal, the control computer operable to determine a fuel command based on the engine speed and fuel demand signals, the control computer determining a predicted pump command based on current values of the pressure signal, the engine speed signal and the fuel command, the control computer logging a fault code if a difference between a current value of the pump command signal and the predicted pump command is greater than a threshold level.
In accordance with yet a further aspect of the present invention, a method of diagnosing a fuel system of an internal combustion engine comprising the steps of sensing a fuel demand signal, sensing an engine speed signal, sensing a pressure signal indicative of fuel pressure within an accumulator forming a portion of a fuel system, determining a fuel command based on the fuel demand and engine speed signals, determining a fuel pump command based on the fuel demand and pressure signals, the pump command activating a fuel pump to supply fuel to the accumulator, determining a predicted fuel pump command based on current values of the engine speed signal, the pressure signal and the fuel command, and logging a fault code if a difference between a current value of the pump command and the predicted pump command is greater than a threshold value.
One object of the present invention is to provide a system for diagnosing failure conditions in an electronically controlled fuel system.
Another object of the present invention is to provide such a system for diagnosing in-range pressure sensor failures.
A further object of the present invention is to provide such a system for diagnosing fuel pump injector blow shut failures.
Yet another object of the present invention is to provide such a system for diagnosing failure of one fuel pump in a dual pump fuel system.
Still another object of the present invention is to provide such a system for diagnosing overpumping of high pressure fuel to the electronically controlled fuel system.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.